propertygrid 中的 TypeConverter 仅从字符串转换，而不是

Question

访问 propertygrid 时，仅调用 ConvertTo 方法（多次）。这会正确返回“Foo!”属性网格中的字符串。当我单击编辑时，出现异常 Cannot conversion object of type Foo to type System.String.（不完全是，已翻译）。 ConvertFrom 方法没有被调用，有什么线索吗？该错误表明它正在尝试转换为字符串，而不是从字符串。

我想当我想编辑这个对象时，它必须从 Foo 转换为字符串，并在完成编辑后返回。

StringConverter 类：

public class FooTypeConverter : StringConverter {
    public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value) {
        return new Foo((string) value);
    }

    public override object ConvertTo(ITypeDescriptorContext context, CultureInfo culture, object value, Type destinationType) {
        return "Foo!";
    }

    public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType) {
        return true;
    }

    public override bool CanConvertTo(ITypeDescriptorContext context, Type destinationType) {
        return true;
    }
}

正在访问的属性：

Foo _foo = new Foo();
[Editor(typeof(System.ComponentModel.Design.MultilineStringEditor), typeof(UITypeEditor))]
[TypeConverter(typeof(FooTypeConverter))]
public Foo Foo {
    get {
        return _foo;
    }
    set {
        _foo = value;
    }
}

Answer 1

重新更新您的信息；这是一个应该作为填充程序工作的 FooEditor：

class FooEditor : UITypeEditor
{
    MultilineStringEditor ed = new MultilineStringEditor();
    public override object EditValue(ITypeDescriptorContext context, IServiceProvider provider, object value)
    {
        Foo foo = value as Foo;
        if (foo != null)
        {
            value = new Foo((string)ed.EditValue(provider, foo.Value));
        }
        return value;        
    }
    public override UITypeEditorEditStyle GetEditStyle(ITypeDescriptorContext context)
    {
        return ed.GetEditStyle();
    }
    public override bool  IsDropDownResizable {
        get { return ed.IsDropDownResizable; }
    }
}

您显然需要关联它：

[TypeConverter(typeof(FooTypeConverter))]
[Editor(typeof(FooEditor), typeof(UITypeEditor))]
class Foo { /* ... */ }

Answer 2

无法复制；对我来说效果很好；您应该测试 destinationType 和 value 类型，顺便说一句 - 但这并不能阻止它调用 ConvertFrom。您是否有一个完整的示例（可能基于以下内容）显示它不调用ConvertFrom？

using System;
using System.ComponentModel;
using System.Globalization;
using System.Windows.Forms;
public class FooTypeConverter : StringConverter {
    public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
    {
        return new Foo("FooTypeConverter.ConvertFrom: " + Convert.ToString(value));
    }
    public override object ConvertTo(ITypeDescriptorContext context, CultureInfo culture, object value, Type destinationType)
    {
        return "FooTypeConverter.ConvertTo: " + ((Foo)value).Value;
    }
    public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
    {
        return true;
    }
    public override bool CanConvertTo(ITypeDescriptorContext context, Type destinationType)
    {
        return true;
    }
}
[TypeConverter(typeof(FooTypeConverter))]
class Foo
{
    public string Value { get; set; }
    public Foo(string value) { Value = value; }

    public override string ToString()
    {
        return "Foo.ToString";
    }
}
class Test
{
    public Foo Foo { get; set; }

    [STAThread]
    static void Main()
    {
        Application.EnableVisualStyles();
        using(Form form = new Form())
        using (PropertyGrid grid = new PropertyGrid())
        {
            grid.Dock = DockStyle.Fill;
            grid.SelectedObject = new Test { Foo = new Foo("Main") };
            form.Controls.Add(grid);
            Application.Run(form);
        }
    }
}